Bridge-truss



(No Model.)

B. TEACHER.

Bridge Truss. I No; 242,396. Patented May 31,1881.

INVBNTOR %a 0M WITNESSES: AQWWJJZW ATTORNEYS.

UNITED STATES PATENT OFFICE.

EDWIN TEACHER, OF PITTSBURG, PENNSYLVANIA.

BRlDGE-TRUSS.

SPECIFICATION forming part of Letters Patent No. 242,396, dated May 31,1881.

Application filed July 16, 1880.

To all whom in? may concern:

Be it known that I, EDWIN THAoHER, a citizen of the United States,residing at Pittsburg, Allegheny county, in the State of Pennsylvania,have invented useful Improvements in Combination and All-IronBridge-Trusses, of which the following is a specification.

By combination-truss is meant one in which the top chord and end strutsare wood, the bottom chord, ties, and suspenders iron, and theintermediate struts either wood or iron.

The object of my invention is to overcome the defects common to agreater or less extent in all forms of triangular or quadrangular trussnow in use, of which the following may be named:

First. In all combination quadrangular trusses (trusses containingquadrangles the sides of which are all connected with each other andwith diagonals that cross each other and join opposite angles) both mainties and counter-ties are affected by temperature, the latter frequentlyto the extent of half their breaking strength.

Second. In double and triple intersection trusses there is ambiguity ofstrain-that is to say, there are no means of finding what the actualstrain on a member is. This is also true of any truss in which a weightcan find its way in more than one direction to the masonry or points ofsupport.

Third. Counter-ties are liable to be overstrained in adjustment byunskilled workmen.

Fourth. Triangular trusses have sometimes tension and at other timescompression on braces near the center. When the greater of these strainsis compression, a wooden brace with iron tensile connections isgenerally used in combination-trusses. If, on the other hand, tension ismuch the greater strain to which the brace is subjected, flat barsconnected with zigzag bracing are generally used. Both of theseexpedients are objectionable, the former owing to strains by temperature011 the connections and the latter to frequency of damage by handling.

Fifth. Both quadrangular and triangular trusses as usually constructedhave each end of the floor-beam 0r cross-girder on which the track orflooring rests supported by two suspenders, which are short links orbars con- (No model.)

nectin g the endof the floor-beam to joint above. These suspenders aregenerally a considerable distance apart, in combination triangular, twofeet six inches being. not uncommon. The reason of this is, that eachjoint is made up strut,

.tie, chord, and floor-beam suspender. The

thrust coming down the strut from other parts of the truss, togetherwith the weight suspended at the floor-beam, is taken by the tie andcarried on toward the support. Now, in order to avoid a very large pinat the joint or excessive bending strain upon it, it is necessary thatthe connection of floor-beam susponder on the pin be made near or incontact with that of the tie, the latter being in pairs, and from thenature of the truss cannot be brought close together. The deflection ofa floor-beam when the load comes upon itcauses an excess of weight to bethrown upon thein- 'ner suspender, and relieves the outer one to acorresponding extent. This unequal strain is conveyed by the suspenderthrough the pin on which it hangs to the various members of the truss,whose unequal extension or compression gives rise to distortion andcrossstrains.

Sixth. Adjustable counterties in quadrangular trusses and trussed tiesin triangular trusses are "cry expensive in workmanship.

Seventh. The large variation in top-chord sections in the differentpanels of most combi nation-trusses renders iron packing difficult andexpensivethat is to say, the strain on the chordincreases rapidly towardthe center, where a much larger section of timber is required than atthe ends and as the chord, as a whole, is always made of uniform widthand depth from endto end, the variation in section can only be made byallowing much larger spaces between the sticks composing the chord atthe end than at the center. make these sticks act together and about theaxis of the chord as a whole, it is necessary to connect them by keys orpacking, by which any strain on one stick will be transmitted throughthe keys to all the other sticks of which the section is composed;otherwise each stick will bend about its own axis and its strength hethereby much diminished. If the spaces between the sticks are small, therequired connection can be easily and cheaply made by In order tomeansof lightcast-iron keys but if the spaces are large the keys becomemassive, and their effectiveness at bestis much impaired. WVooden keysare generally used in these bridges, but at the expense ofgreatly-reduced durability, for it is a well-known fact that wood incontact with wood soon decays, but that wood in contact with iron is notthus affected.

Eighth. In quadrangular trusses the sudden change of strain fromcounter-tie to opposite main tie, or the reverse, as a train passesover, and the consequent racking of parts, is very in urious.

My improved truss can be made free from the foregoing objections.

Itconsists of a primary triangular truss composed of top and bottomchords, together with a web of struts and ties, arranged in the form oftriangles, free to change figure from the effects of temperature. Thecenter ties extend each over a greater number of panels than any strut,ovcrnot less than two, and over not more than the number in halt-spanless one. The panel-points intermediate between the tops of the centerties, and not at joints of the primary truss, are supported by verticalsuspenders, or partially supported by pairs of inclined suspenders, fromthe top of the center strut, and the balance supported from theoutermost limits ofsuspension. The inclined suspenders are connectedwith each other, but have no fixed connection with the bottom chord, norwith the center ties at intermediate points of intersection.

Figures 1 to 5, inclusive, represent side ele-' vations ofbridge-trusses embodying my invention; and Fig. 6 represents, in detail,a side elevation of intermediate panel-point, D.

In Figs. 1, 2, and 3 the top and bottom chords, together with themembers F A, AB, and B G,constitute the primary truss. In Figs. 4 and 5it consists of the same members, with the addition of the two diagonalsbetween A F and the end of span.

All parts not specified above as belonging to the primary truss aresuspended from it or used to supportintermediate panel-points. A A maybe called the limit of suspension.

A B are the center ties, connected with the top chord at A and with thebottom chord at B.

O B is the center strut, either vertical, as in Figs. 1 and 3, orsloping toward the end, as in Figs. 2 and 4, or toward the center, as inFi 5. The struts may be vertical or inclined, as best fulfills therequirements of any particular case.

In Figs. 1, 2, 3, and 4 the center ties meet in the bottom chord. InFig. 5 the center struts meet in'the top chord.

E E are intermediate panel-points, supported by the vertical suspendersO E from the top of the center strut, G B.

D D are intermediate panel-points, supported by inclined suspendersdirectly or indirectly from the points A and C of the primary truss.

These suspenders are in pairs, connected with each other at D but theyhave no fixed connection with the center ties, A B, nor with the bottomchord. In Fig. 6 the broken bar below D is the chord, supported, asshown by the suspenders, by means of a stirrup attached to the pinabove. It may,however, be done, if desired, by means of a seat on thefloor-beam below; but whatever method is adopted, the joint at D must beleft free to move longitudinally unrestrained by the chord. Thesepanelpoints may each be supported by pairs of inclined suspenders A Dand D (J, leading directlyfrom them to the points A and O of the primarytruss, as shown orsome of them may be thus supported and others of themas before described.

If the length of span permits, the center ties may each extend over fouror more panels, and a greater numberof intermediate panel-points besuspended. A A are the limits between which intermediate suspended panelpoints aid in overeomin g reversed strains in the center braces, and thecenter ties may always extend over a suflicient number of panels toaccomplish this object when desired.

The weight at any intermediate panel-point, D, is conveyed by theinclined suspenders to the joints A and O of theprimary truss in proportions inversely as its horizontal distance from thosejoints. Thepartgoing toO increases the compression in the center strut, O B, as doesalso the weight from any intermediate panel-point, E,conveyed throughvertical suspenders to the same point. Any compression in the centerstrut due to intermediate suspended panel-weights gives tension on thecenter ties on both sides of the center, and opposes reversed strains inthe center braces due to partial rolling loads. The only panel-points onwhich rolling load either side of the center can tend to producereversed strains in the center ties are those at A, or between thosepoints and the truss-supports. The compression in the center strut andtension in the center tie increases as the points A are moved toward theend of span, and the distance between these points can, if desired,always be made sufficient to overcome all reversed strains in the centerbraces. Any panel load produces compression in the top chord and tensionin the bottom chord.

In Figs. 1 and 3 the maximum strain in either chord, which occurs whenall joints are loaded, is uniform throughout its length, and in all thetrusses the maximum strains in the different panels of the top chord areso nearly uniform that in combination-bridges the section could be madeuniform without material increased cost.

The bottom lateral system may consist oflongitudinal and diagonaltension-rods connected with transverse floor-beams, which act as thestruts of the system; or it may consist of transverse struts anddiagonal tension-rods connected with longitudinal floor-beams sus'pended from the panel-points.

From the preceding description it will be understood how the advantageswhich my truss possesses over the prevailing styles previously claimed,but not described, are gained.

As there are no confined quadraugles, and as no wooden braces havingiron tensile connections need be used, temperature strains can beavoided.

As the suspenders act independent of the chord at D, the weight at thosepoints can reach the joints A and O of the primary truss in no other wayor manner than as described, and as the primary truss consists of asingle system of triangular figures, a weight at any joint of it can goin but one way to either point of support; consequently there can be noambiguity.

As thelength of any one or more of the members of the primary truss orof the suspenders can be changed and the work still come together asreadily as before, adjustments are not called for.

As the pairs of inclined suspenders at D and of center ties at B can beplaced as near together as desired and in contact with the floor-beamsuspender between them, the latter can be made of a single bar at thecenter of pin without increase of cost.

The vertical suspenders O E can be made a single bar passing through thefloor-beam it the latter is of wood, or in pairs connected by pin at E,with a single loop-suspender between them connected with the floor-beam,if an iron floor-beam with asingle web is used.

As in all the figures a top chord of uniform section would be used incombination-bridges, and the spaces between the chord-sticks he madeuniform and as small as desired, packing blocks or keys of iron can beused at a minimum expense.

My improved truss is more economical in workmanship than others, owingto the shorter and smaller pins, the absence of sleeve-nuts oradjustments of anykind, and its freedom from zigzag bracing. It is alsofully as economical 4 5 in material as any of the prevailing styles.

As there are no adjustments to get out of order, it requires little orno superintendence after it is once erected, and as every part isstrained under all conditions of load, and as no distortion can changethis relation of parts, less repairs will be required and a longer lifeinsured than in counterbraced forms. It has all the advantages withoutthe disadvantages found in most of the trusses now in use.

I claim as new and desire to secure by Letters Patent- 1. A bridge-trussconsisting of a primary triangular truss, composed of top and bottomchords, and a web of struts and ties arranged in the form of trianglesfree to change figure from the effects of temperature, substantially asset forth, the center ties extending each over a greater number ofpanels than any strut,

over not less than two, and over a number not exceedingthe number inhalf-s pan less one, the panel-points intermediate between the tops ofthe. center ties, and not at joints of the primary truss, beingsupported by vertical suspenders, or partially supported by pairs ofinclined sus- 7o penders, from the top of the center strut, and thebalance from the outermost limits of suspension, said inclinedsuspenders being also connected with each other, but having no fixedconnection with the bottom chord, nor with the 7 5 center ties atintermediate points of intersection.

2. Inclined suspenders in combination with a triangular truss having abottom chord always in tension, which support the weight of that chordwithout having any fixed connection with it by means of a stirrupattached to the pin above, substantially as set forth and described.

EDWIN THAOHER. Witnesses:

NATHANIEL GREEN, 0. A. JACKSON.

